--- a/devtools/client/inspector/markup/test/browser_markup_tag_edit_08.js
+++ b/devtools/client/inspector/markup/test/browser_markup_tag_edit_08.js
@@ -21,20 +21,23 @@ add_task(function* () {
   yield testModifyInlineStyleWithQuotes(inspector, testActor);
   yield testEditingAttributeWithMixedQuotes(inspector, testActor);
 });
 
 function* testCollapsedLongAttribute(inspector, testActor) {
   info("Try to modify the collapsed long attribute, making sure it expands.");
 
   info("Adding test attributes to the node");
-  let onMutated = inspector.once("markupmutation");
+  let onMutation = inspector.once("markupmutation");
   yield testActor.setAttribute("#node24", "class", "");
+  yield onMutation;
+
+  onMutation = inspector.once("markupmutation");
   yield testActor.setAttribute("#node24", "data-long", LONG_ATTRIBUTE);
-  yield onMutated;
+  yield onMutation;
 
   yield assertAttributes("#node24", {
     id: "node24",
     "class": "",
     "data-long": LONG_ATTRIBUTE
   }, testActor);
 
   let {editor} = yield focusNode("#node24", inspector);